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Physical determinants of strong voltage sensitivity of K+ channel block

Nature Structural & Molecular Biology volume 16, pages 1252–1258 (2009)Cite this article

Abstract

Strong voltage sensitivity of inward-rectifier K+ (Kir) channels has been hypothesized to arise primarily from an intracellular blocker displacing up to five K+ ions from the wide, intracellular part of the ion conduction pore outwardly across the narrow ion-selectivity filter. The validity of this hypothesis depends on two assumptions: (i) that five ion sites are located intracellular to the filter and (ii) that the blocker can force essentially unidirectional K+ movement in a pore region generally wider than the combined dimensions of the blocker plus a K+ ion. Here we present a crystal structure of the cytoplasmic portion of a Kir channel with five ions bound and demonstrate that a constriction near the intracellular end of the pore, acting as a gasket, prevents K+ ions from bypassing the blocker. This heretofore unrecognized 'gasket' ensures that the blocker can effectively displace K+ ions across the selectivity filter to generate exceedingly strong voltage sensitivity.

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Figure 1: Kinetic scheme and Kir structure.
Figure 2: Crystal structure model of the cytoplasmic pore.
Figure 3: Ions and surrounding water molecules.
Figure 4: Effects of mutations at Phe254 on spermine block of Kir2.1 channels.
Figure 5: Identification of mutations in M2 that affect spermine affinity of the deep site in Kir2.1.
Figure 6: A quintuple mutation abolishes spermine block of Kir2.1.
Figure 7: Deleting the cytoplasmic loop lowers the valence of Kir2.1 block.
Figure 8: Structural comparison of the isolated Kir3.1 cytoplasmic pore and the Kir chimera.

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Acknowledgements

We thank L. Jan (University of California, San Francisco) for sharing Kir2.1 and Kir3.1 cDNAs, J. Yang (Columbia University) for Kir2.1 cDNA in the pGEM-Hess vector; R. MacKinnon (Rockefeller University) for Kir3.1 cytoplasmic pore cDNA construct and for teaching molecular replacement method to Z.L.; K. Baek, R. Dominguez, K. Ferguson, S. Lee, S. Li, K. Schmitz and Y. Zhou for technical assistance and/or discussion, staff at CHESS A1 and NSLS X25 for technical service; and P. De Weer for review and discussion of our manuscript. This study was supported by a grant (GM55560) from the US National Institutes of Health and by the Howard Hughes Medical Institute.

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  1. Yanping Xu and Hyeon-Gyu Shin: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Physiology, Howard Hughes Medical Institute, University of Pennsylvania, Philadelphia, Pennsylvania, USA

    Yanping Xu, Hyeon-Gyu Shin, Szilvia Szép & Zhe Lu

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Contributions

Y.X., H.-G.S. and Z.L. performed the experiments; Y.X., H.-G.S., S.S. and Z.L. analyzed the data; Y.X. and Z.L. wrote the manuscript.

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Correspondence to Zhe Lu.

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Xu, Y., Shin, HG., Szép, S. et al. Physical determinants of strong voltage sensitivity of K+ channel block. Nat Struct Mol Biol 16, 1252–1258 (2009). https://doi.org/10.1038/nsmb.1717

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